Pressurized storage container and method of operating same



March 15, 1960 E. s. MILES PRESSURIZED STORAGE CONTAINER AND METHOD OF OPERATING SAME Filed April 14, 1954 3 Sheets-Sheet l INVENTOR. Elf/il' J www March 15, 1960 E. s. MILES 2,928,249

PRESSURIZED STORAGE CONTAINER AND METHOD OF OPERATING SAME K Filed April 14, 1954 3 Sheets-Sheet 2 March 15, 1960 E. S.l MILES PRESSURIZED STORAGE CONTAINER AND METHOD OF OPERATING SAME Filed Aprilv 14. 1954 3 Sheets-Sheet 3 rREssUnIzED STORAGE CONTAINER AND Marr-ron or oPERATlNG SAME Elburt S. Miles, Oklahoma City, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware- Application April 14, 1954, Serial No. 423,023 11 Claims. (ci. S1-.5)

This invention relates to a pressurized storage container and a method of operating same. In one of its as- -pects this invention relates `to an improved underground storage system for storing liquefied gases under pressure. In another of its aspects, this invention relatesfto an improved apparatus and method for sealing an underground storage system while inserting or withdrawing pump from the underground storage system. l

Constantly expanding production offliquefied petroleum gas has created a definite problem in providing suitable storage facilities for this material. Due to the high vapor pressure of liquefied petroleum gas, particularly propane, the cost of storage in surface equipment, such as'steel tanks, becomes excessive due to the massive construction required to withstand the vaportpressure of the stored material in a safe manner. The problem becomes eX- tremely acute Vwhere it is necessary to store large quantities of such materials during the off-season.; In addition to the expense involved, the use of steel tanks is limited by shortages in production.

In order to'overcome some of these difliculties, it has been proposed to store liquefied petroleum gas in porous water bearing formations, in water-leached caverns in salt formations or in abandoned mines in impermeable shale or in limestone formations. Further, underground concrete storage tanks and buried sections of pipe have been used to a limited extent in the storage of liquefied petroleum gas.

In a copending application, Serial No. 348,344,7filed April 13, 1953, by Edwin E. Reed, entitled Pressurized Storage System and Method of Operating there is disclosed an underground storage system for liquefied petroleum gas which is capable of storing extremely large quantities of this material at a very small unit cost and the present invention relates to a method and means for sealing such a system against product losses during equipment changes. The storagesystem therein and the storage system and method of operating herein are not limited to the storage of liquefied petroleum gas, but are applicable to the storage of any liquefiable gas such as ammonia, carbon dioxide, and the like. Further, the present invention is not necessarily limited to underground storage systems and can be employed where steel tanks are used as the pressurized containers. n

There are many methods of removing'liquefied gas from a storage container. For example, it is well known that a liquefied gas can be forcedfrom a chamber by introducing compressed gas above the liquid.

In other instances, displacement by a second non-contaminating liquid of greater density can be employed. .One method, and a more generally preferred method, for removing a liquefied gas from storage is byA means of a centrifugal pump. The pump is usually contained within the pressurized vcontainer and can be one wherein the motor driving the pump is also submerged, or of the type driven by a rotating shaft attached to a motor outside-of the container. It is recognized that such pumps will have to be pulled from the container from time to time for repair or Ice Patented Mar.. 15,"19695- replacement. To do this, some means must be provided to' prevent the loss of large quantities of vapor from the container. There is disclosed in Serial No. 348,344,l mentioned above, an apparatus and method to insure that the container can be tightly sealed during the time the pump is being operated or being inserted or withdrawn.

In particular, there is disclosed in Serial No. 348,344, a spring-operated, normally-closed valve at the bottom of the casing, which is within a central shaftv connecting the surface of the earth to the caverns, the valve stern of which valve is displaced by the pump body and thereby the valve is opened, when the pump is lowered into operating position. Accordingly, when the pump body is raised, the valve closes thereby sealing the storage container. Inthe event that the valve should fail to close properly when the pump body is raised, however, other means are ret quired to seal the container while inserting or withdraw ing the pump.

It is, therefore, an object of this invention to provide an improved underground storage system.

It is another object to provide an improved apparatus and method for sealing a pressurized container.

A still further object is to provide a method for oper-A ating an underground storage cavern for the storage of liquefied petroleum gases to allow removal and replacement of a pump and the associated tubingstring, while maintaining the cavern seal and preventing uncontrolled venting of the stored product. Y

`I have now discovered that an underground storage system for storing fluids under pressure, for example, liquefied petroleum gas, wherein a subsurface cavern is connected to the ground level by a shaft containing a casingstring having within it a tubing which suspends a pump near the bottom of the shaft for lifting the'stored fluids to the ground level, can be effectively sealed against loss of stored fluids by introducing an inert fluid, which is irnmiscible with and of greater density than the stored fluid, for example, water, to the casing to form a column of the inert fluid within the casing which balances the pressure of stored fluid in the cavern. Since the inert fluid is introduced to the casing at a pressure greater than the'pressur'e of the stored fluid, the inert fluid collects in the bottom of the shaft and in the casing, and by simultaneously venting stored fluid which is entrappedabove the inert fluid in the casing to equalize thepressure in the casing and in the cavern, a column of -inert fluid is obtained in the casing which balances the pressure of stored' rfluid in the cavern, at which time the cavern is sealed, al-

lowing the pump and associated tubing to be withdrawn f a lower region'thereof, by partially filling the conduity with an inert fluid which is immiscible with and of greater` density than the stored liquid, therebysealing the contents; of the container and entrapping stored liquid in the conduit above the inert fluid, and thereafter venting the en-v trapped liquid and concomitantly therewith introducingl more inert fluid to the conduit until the pressure of the hydrostatic head of the inert fluid above the level of ther stored liquid in the container equals the pressure exerted' by the vapor pressure of the stored liquid and the hydro-rv static head of the stored liquid within the container.-

Various other objects, advantages and features of the invention will become apparent from the followingde tailed description taken in conjunction with the panying drawing, in which:

' Figure 1 is a vertical sectional view, partially in e1eva-A accomf ording to a preferred modification of my invention..

an underground storage system of the present invention includes at least one storage cavern which contains at leastone chamber 10. The caverns can be constructed in a variety of different ways as illustrated in the copending application of Leonard P. Meade, Serial No. 314,541,

filed October 13, 1952, now abandoned, which cepend-v ing application also discloses a preferred modification of the present invention. For example, a single large cave can be excavated, or a number of smaller caves can be formed and interconnected in any suitable manner. As shown, large chamber communicates by means of tun nels V11 and 12 with an enlarged vertical shaft 13 extending from the surface of the earth Vto a region adjacent the cavern. Other Caverns in the system are not shown in the drawing. The storage chambers can be of any geometric shape.

' Disposed in each tunnel 11 is a drain pipe or header 14, and the headers of all the caverns extend through the respective tunnels and communicate with the shaft 13. Each storage chamber is provided with a drain pipe 15 which at its lower end is connected to the header l-i and which extends upwardly into the associated storage chamber 10. Thus, should the tunnel 11 become choked with rock, or dirt due, for example, to caving, the main storage portion of the chamber still communicates with the shaft through its associated pipe 15 and header 14. As a result, should caving occur while duid is stored within the chamber, the uid can drain out through the described pipe and header, and the main storage portion of, the chamber is available for further service even when caving occurs.

Although such drain pipes are very advantageous in many installations, they may not be required in cases Where the formation is not subject to caving.

`Forming a part of each cavern is an upper tunnel 12, each upper tunnel being connected to one of the storage chambers 1,0 and communicating with shaft 13. Die posed in each tunnel 12 are a pair of vent pipes v7.6 and 1 7 communicating with shaft 13 and the adjacent chamber `10. The purposerof these vent pipes is to provide ventlng of Vthe entire underground storage system to equalize pressure'throughout. lt will be evident that, lff'desired, tunnel sections 12 can be eliminated and the described communication between the upper part of the storage chambers and the shaft can be effected solely by the vent pipes 16 and 17. Conversely, the vent pipes 16, 17 could be eliminated and venting effected through the tunnel. Where different types of caverns are used any suitable means can be employedk to equalize the vapor pressure above the liquid to be stored in the various cavrns or storage chambers of the system. One or more offthe Caverns is provided with a drilled hole 18 extending fromv the surface of the earth to the top of the associated cavern through which material is introduced into the system for storage. The lling mechanism at thesurface, not shown, is of a nature to prevent loss of pressure from the system. Suitable mechanism is il lstrated in the aforementioned copending application of Leonard P. Meade, Serial No. 314,541.

The shaft 13 incorporates pump mechanisms, to be hereinafter described in detail, forV lifting the stored iiuid from the bottom ofthe shaft to the surface from whence it isA passed to transportation and marketing outlets, or other desired use. In operation, therefore, the material erns by lling means V18, or such lling means or pipe can extend to the bottom of the cavern. Material Withdrawn from storage ows through the lower tunnel 11 and/or the header 14V to the shaft 13 where it is lifted to the surface for use as described. Materials such as liquefied petroleum gas have` a high vapor pressure and the thickness ofthe earth layer above the caverne is effective in `containing this high vapor pressure without the use of steel tanks or a lining for the cavern. An advantageous location for such a storage system is in an impermeable shale formation, whereby a long period of trouble-free operation is assured.

Referring again to Figure l, two strings 2t) and 21 of casing extend from the surface of the earth through means hereinafter 'described and the lower portion of shaft 13 into a well 22 formed at the bottom of the shaft. It will be noted that the well 22 is below the level of the tunnels 11 and Caverns so that fluid can flow from each one of the storage chambers into the well. At the bottom of the well, the casing strings 20 and 21 are received Within enlarged sections 23 and 24, respectively, of pipe which are anchored in a mass 25 of cement at thebottom of the well. Disposed at the lower ends of casing strings 20 and 21 are valves 26 and 27 respectively, and immediately above these valves are pumping units Y ZS-and 29.- Pump 28 is a multiple stage pump supported Within casing 20 by means of tubing 30 and driven by rod 31 extending through tubing 3? to the surface. 'Pump 33 is supported within casing 21 by means of tubing 32 and incorporates a motor 29a which is actuated by' suitable electrical current source at the surface. Both pumps yare actuatable to lift the uid stored within the.

system through the shaft to the surface.

Referring now to Figure 2 of the drawing, it will be noted that a tubular metal liner 4t? formed, for example, from steel is provided at the top of the shaft ant this liner is anchored by a mass fl-l'of cement disposed about the exterior of the liner. The liner extends a substantial distance downward in the shaft, if desired, or to a location just above the upper tunnels 12 for the purpose of supporting the walls of the shaft and substantiallyor completely eliminatingV the flow of water or other liquids into the shaft. rhe liner, of course, also prevents the escape of the stored material. The mass of cement includes an enlarged rounded upper section 42 adjacent the surface of the earth and supporting and anchoring the liner 4t), a generally cylindrical portion 43 surrounding the body of the liner 46, and a. lower inwardly protruding portion 44 adjacent the bottom of the liner. The top of the liner protrudes a short distance above the earth and is closed by an enlarged ilat plate or Well headV 45. It will be evident that the liner di?, Well head 45 and mass 41 of cement constitute collectively means for sealing the shaft 13 at a region above the level of the lower tunnels 11 and upper tunnels 12. A manhole closed by a cover 46 is provided in the liner 40 for access into the storage system for any desired purpose.

With respect to pump 28, it will beY noted that the casing string, tubing string, and drive rod all extend upwardly through the shaft 13, the liner 4l), and the well head 45 to the surface, where these parts all pass through a valve Sil, Eigure 2, on top of the well head. 'immediately above valve 50 is a casing head'51 from which the casing string is hung. Y

Casing head 51 can be any of the Well known casing heads in the well drilling art which provide support for the casing and provide a seal between the casing and shaft wherein the casing is hung. A suitable casing'head is shown in detail in Figure 3.

Referring to Figure 3, it will be noted that the casing head includes a generally cylindrical body 52 bolted to an adjacent flange of valve 50 and provided with pipes 53 and 5,4 which provide access to the space between the asing'and the shaft. Valve 48 controls pipe 53 and valve 4,9y controls pipe 54. The upper end of casing string 20 i s threaded to a tapered annular block 55 which engages acomplementary tapered surface 56 of the body 52, the block being provided with a plurality of sealing gaskets 57 and held in positio'n by bolts 58. The gaskets 57 seal the region between the body 52 and casing string 20, this region'communicating through valve V50 with the top portion of shaft 13. A pipe 60 is threaded to the top of block 55, this pipe extending upwardly to and supporting a valve 61, Figure 2. Pipe 60 is provided with pipes 91 and 93 which communicate with the interior of pipe 60 and, since pipe 60 is in effect an extension of casing 20, see Figure 3, which provide access to casing 20. A Valve 9S controls pipe 91 and a valve 97 controls pipe 93. The tubing string 30 with its concentric drive rod 31 extends through pipe 60 and valve 61 to a combination tubing head and slip joint 62 shown in detail in Figure 4. Tubing head 62 provide means for supporting the tubing string 30 and pump unit 28 and means for sealing the region between tubing 30 and tubing head 62 when tubing 30 is raised or lowered. e,

"Referring to Figure 4, it will be noted that the tubing head includes a generally cylindrical body 63, the lower end of which rests upon and is supported by an adjacent flange of valve 61. The upper end of the tubing'30 isV threaded to a flanged block 64 which is bolted to' a flange 65 secured to the body 63. Any annular member 66 tits between the body 63 and, the tubing 30, this 'member being provided with an annular sealing gasket 67. Secured to the flange block 64 is a pipe 7@ communicating with the interior of the tubing and provided with an outletconduit 71. ,I Immediately above conduit 71 is a sealing member 72through which extends drive rod 31 of the pump, this rod being driven by an electric motor 7 3 at the top of the assembly. A line 99, and controlling valve 101 therefor, extends from an opening 103 in pipe 60 to seal assembly 72, establishing communication therefrom to the casing and allowing liquid fro'm the seal to drain back into the system. e

Injassembling and operating the apparatus, valve 50 is openedvand the casing string is hung from casing head 51 sci that it extends downwardly through valve 50 to its position within the pipe23, Figure l. lower lend, of the casing is the valve 26 which is normally clo'sed so tha-t, once the casing is inserted and the casing head sealed, no material can pass through casing to the surface nor` between the casing and the body 52. Thereupon, thejtubing string and drive rod are lowered into the well section by section, it being understood that the pumpV 28 is secured to thel lowermost section of tubing. This process continues until the pump is disposed a short Attached to the o'f the'pipe 23 fluid enters a lower section 80, Figure 1,. of the valve 26, this valve section being centered by a series of vanes 81 protruding from the wall of the pipe 23. The valve 26 is biased in a closed position by a spring (not shown) and no fluidrcan enter casing 20v The pump, thereupon, lifts the uid through the tubing, the surface structure 50, 61 and '62 and to and out through discharge conduit 71. Reference is made to Figure 6 of the above-cited copending application Serial No. 348,344 for the details of the construction of valve 26.'

The construction of the pump unit 29 and casing string 21 is similar to that described in connection with the pump unit 28 and casing string 20. In thisY construction, the motor 29a, Figure 1, is downhole, and is mechanically connected to pump 33. The casing string 21 and' the tubing string 32, supporting the pump-motor assembly,

distance above the valve 26, at which time the annular Y member 66, rl-Ti'gvre 4, and sealing gasket 67 are positioned at the upper vend of the cylindrical body sectioncontaining them, and the flanged block 64 with its attached pipe 70 is' positioned a short distance above the cooperating flanged member 65. At this time, the interior of the casing is, pressurizedas by connecting valve 48 and valved pipe 91, Figure 2, that is, the pressure in the casing is equalized with the pressure in the underground storage system. Thereupon, theltubing is lowered to its final position, thereby causing the pump body to engage the valve 26 and open it. Due to the annular member 676 and.

sealing gasket 67. the vapor in the casing cannot escape during the period when the tubing and pump are lowered into the final operating position, at whichl time the flanged block 64 is bolted to the part ,65 and the system is sealed. l" Thereafter, when the motor 73 is energized, the resultingrotationy of rod 3,1,and pump 28 lifts fluidy to the surface of the ground.

.Referring to Figures l and 2,*it will be noted that fluid passes, into the pipe 23 from the tunnels 11 and headers4 14i leading to thestorage chambers. From .the bottom extend upwardly through the shaft 13, the liner 40, and the well head 45 through a valve 50a, a casing head 51a, a pipe 68a, and a valve 61a corresponding in structure and function to the similarly numbered Vparts described in connection with the casing string 20. Positioned above valve 61a is a tubing head and slip joint 62a which is similar to vtubing head 62 but which is modified to pro'- vide for electrical leads which supply power to motor 29. Reference is made'to Figures 7 and 8 of Serial No. 348,344, cited abo-ve, forV the'details of tubing head and slip joint 62a.

In the event, it is necessary to remove the pump unit.

for servicing, a `procedure is set forth in Serial No. 348,344, referred to above, based on the closure of valve 26 when tubing 30 is lifted to remove the pump 28 froml engagement with valve 26. However, when this procedure is followed, valve26 could fail to close for many reasons,

for example, a piece of rock or other foreign material can become lodged in valve 26. If this should happen, it is necessary to shut off the flow of fluid to the casing to prevent uncontrolled venting of fluid from the caverns when `the tubing and pump unit is raised. In accordance with this invention the casing can be sealed off simply, cheaply and effectively to permit the withdrawal and/or introduction of the tubing and pump unit. ln accordance `with my invention, `the casing is partially filled With an inert fluid, which isimmiscible with and of greater density than the stored liquid. The contents of the undergroundv storage system are thereby sealed from the casing and' stored liquid in the casing isentrapped therein above said inert fluid. The entrapped stored liquid is vented from the casing and, concomitantly therewith, additional inert fluid is introduced to the casing until the pressure of the hydrostatic head of the inert fluid in the casing abovel the level of the stored liquid equals the pressure exerted by the vapor pressure of the stored liquid-and the pressure of Ythe hydrostatic head of the storedv liquid Within the storage system. Thereafter, the pump unitand asso-` ciated Vtubingr string can be withdrawn or introduced to'v the casing without loss of stored fluid. If valve 26 is to' be replaced, a bridging plug can be set in the casing,k after k Whichnfthe casing can be pulled, utilizing blow-out preventers?? or control heads similar to those used in pulling and running tubing underfpressure in oil and gas wells.

VThe advantages vof my invention will be apparent to those skilled, in the art of underground storage of liquefied petroleum gases. Water is admirably suited for serving `as the inert fluid when liquefied petroleum gases are the stored liquids. Thus, an inexpensive, readily available material, such as Water, `can be used to accomplish the objectives of this invention. Where other liquefied,

normally-gaseous uids are stored in an imderground "2" storage system, such as liquid ammonia or liquid carbon dioxide, Aa suitable immiscible liquid is used, such as brine. lVery little extra equipment is required,'as will become apparent from the discussion hereinbelow. Since well 22 extends below the oor of the caverns and since well 22is lined with cement 25, contact of the water with the floor and walls of Vthe caverns is prevented. This is important when the storage system is constructed in formations which are subject to caving and spalling when exposed to water. Also, the well permits the seal to be effected with a minimum amount of water. My invention can be used when the storage system is constructed Without a well or sump at the bottom of the shaft, but

to seal the bottom of the casing, itis necessary to till the cavernwith water up to the bottom of the casing. As was mentioned before, in some formations, water has a deleterious effect and, of course, a much larger quantity of water is required in the event the system is constructed without a well or sump at the bottom of the central shaft.

As was stated heretofore, my invention is broadly applicable to underground storage systems, such as have been described herein. However, a more desirable mancomposition of the stored liquid inthe underground storage system can cause the stored liquidto assume different levels in these places'. 1f, for example, the level of the stored liquid should be higher in casing 2d than in cavern 10, more stored liquid will be entrapped in casing by the introduction of the inert fluid than would be otherwise the case. This is a disadvantage since a greater volume of the stored liquid must be vaporized and vented to obtain the column of inert duid in casing 2i? which is necessary to seal the cavern and balance the pressure of the stored liquid in the cavern. Another disadvantage in having a higher column of stored liquid in casing Ztl than in cavern 10, and consequently an advantage .for equalizing the pressures in accordance with this invention, is that theV higher column of liquid in casing 2.6 could tend to push the inert fluid, initially introducedV to partially iill 1 pipe 23,` out ofV pipe 23 and into well 2?; and possibly onto the iloor of cavern 1d, thus contaminating the stored liquid and damaging rock `formations surrounding the cavern which may be subject to sloughing and spalling when in contact with water..

There is illustrated in Figure 2 the novel apparatus elements required to 'carry out my invention and in particular, the system of apparatus for equalizing the pressure in tubing 30, casing and cavern before introducing the inert fluid and venting entrapped stored liquid.

A valve 1137 is connected to and controls discharge conduit 71. A line M59 connects valve 1:37 to valve 95 thereby establishing communication between the interior of tubing 3i) and the space between tubing 3d and the interior Vof casing 2t). A line 111 is connected to valve 48 and to a T-section 113 installed in line 191,3 thereby establishing communication between the cavern 11i and tubing and casing 20. A pressure gauge 115 and aV valve 117 are also installed in line 109 between valve 9S and T-section 113i. A vent line 119 and valve 121 controlling` line 119'and connected to a TY-section 123 inf.

stalled in line 1tl9 between T-section 113 and valve 167.

Similarly positioned and connected apparatus elements are installed to connect tubing 32 to casing 21 to `cavern 1Q andwhich compriseV a valve 197e.' installed on discharge conduit 71a and a line 161%, line 111e, T-section riz-1a and. -r-secuon 123g.

A source of inert uid under a pressure greatery than the pressure of the stored liquid isconnected by a line 12f7,and a T-section 129 installed in a line 131, which connects valve 97, valve 97a, and the interior of casing strings 20 and 21. Obviously, in the case where the stored liquid is liqueed vpetroleum gas and the inert fluid is water, the pressure on the water can be supplied by suitable pumps, not shown.

Assuming that the underground storage system contains liqueiied petroleum gas7 that the shaft driven pump 28 must be vremoved for servicing and that valve 26 has failed to close when pump 28 and its associated tubing string was partially lifted, my invention is utilized and carried out as follows. Reference to the detailed mechanics of disassembling the superstructure and raising the pipe involved in the foregoing and succeeding operations is omitted, since such operations are completely described in the'copending application, Serial No. 348,344, cited above.

To insure that the level of the stored liquid is the same in tubing 3), casing Ztl and cavern 10, valves 107, 117, 95, and 48 are opened to equalize the pressure through# out the underground storage system and thereby to equalize said liquid levels. The reasons and advantages-y for doing this have been discussed and in some casesv this phase ofthe operation can be eliminated. Thereafter, valve 97 is opened and water is introduced to casing 20, initially, to partially till pipe 23. Sufficient water is ini. tially introduced to pipe 23 to cover the vopening. at the lower end of casingfZii and thereby to seal the cavern liquid from access to casing 2d.y Stored liquid is entrapped above the water in pipe 23 in casing 20. Valve 48 is then closed, thereby isolating the cavern, pressure. from casing 2i) and tubing 30. Thereupon, valve 121 is; partially opened to vent the entrapped stored liquid from casing 20 and tubing Sil, andy concomitantly therewith, additional water is introduced from source 125 to casingA 20. The entrapped stored liquidy is thus vented and additional water added vto casing 20 until a column of Water isrobtained in casing 20 which exerts a pressure equal to the pressure or" the storedliquid inl cavern 10. All of the' entrapped stored liquid in casing 20 will have been vented, and after adding an additional volume of water equal to the volume occupied by the pump and its associated tubing string, the pump and associated tubing string can. be Vwithdrawn without loss of stored liquid from the' storage system.

To insure that the level of water in pipe 23 stays below the cavern oor and above the lower end of casing 20, it is desirable to maintain the pressure in casing 20. during the venting and water-illing operation'such'that the pressure in casing Ztl never exceeds the pressure in cavern 10X: and such that the pressure in casing 20 does not' drop'y lower than 5 p.s.i. below the cavern pressure.

The application of. the present invention to removall and/or insertion of submerged motor pump 29'v is the. same as that described for the removal of the' shaftdriven ,pump 2S, using the a numbered elements of' apparatus.

After removal of the pump, valve 26 can be removed' for repair or replacement by setting a packer o1'. plug in" casing 20, using blow-outv preventers and a lubricaf tor, well-known expedients in theart of drilling oil and gas wells, and then pulling casing` 20 with valve 26 at# tached thereto.

As an example of the application of the present inverttion tok the underground storage system illustrated invk Figures 1 and 2, it is assumed. that cavern 10 ispartially' illed with propane which has a vapor pressure of' 10D" p.s.i.a. at the cavern temperature: It is further `assumed that the upper level of the propane is 45 feet above'tlie' inlet to casing 2@ at the bottom of well 22. The'pressures at this point, i.e., the inlet to casing 20, will befapproximatelyv ll() p.s.i.a. In accordance with: thev inventio'm water is introduced into casingfz20` uutilla'-v` colurm ofi water-*220 feet high vis obtained in casing'." -A column ofs water 220 feet high exerts a pressure of 95.3 p.s.i. which is the pressure exerted by the propane in the cav' ern, i.e., 110 p.s.i.a minus 14.7.

While this invention has been described and exemplified in terms of its preferred embodiment, those skilled in the art will appreciate that modification can be made without departing from thev spirit and scope of the invention.

I claim:

1. A method for sealing a container which contains a stored liquid under pressure so that a pump can be withdrawn from or inserted into said container without loss of pressure therefrom, said liquid exerting a vapor pressure, said container being provided withaclosable conduit extending downwardly through a boundary of "said container to a lower region thereof, which comprises,

. partially filling said conduit with an inert iiuid which is immiscible with and of greater density than said stored liquid, said fluid attaining a level in said container outside said conduit so that said container is thereby sealed by said inert fiuid, stored liquid thereby being entrapped in said conduit above saidinert iiuid, venting said en' trapped stored liquid from said conduit and concomitant'- ly therewith introducing more of said inert fluid to said conduit until the pressure of the hydrostatic head of said inert uid in said conduit above the upper level of said finid outside said conduit plus atmospheric pressure equals the pressure exerted by theabsolute vapor 'pressure of the stored liquid plus the pressure of the hydrostatic head of said stored liquid within said container lon said fiuid outside saidfconduit. y

2. A method according to claim 1 wherein said stored liquid is liquefied petroleum gas and said inert uid is water.

3. A method for withdrawing a pump from and reinserting a pump into a container which contains a stored liquid under pressure, without loss of pressure therefrom, said liquid exerting a vapor pressure', said container being provided with a closable conduit extending downwardly through a boundary of said container to a lower region thereof, said pump being positioned within the lower portion of said conduit, which comprises, partially filling said conduit with an inert uid which is immiscible with and of greater densty than said stored liquid, said fiuid attaining a level in said container outside said conduit so that said container is thereby sealed by said inert fiuid, stored liquid thereby being entrapped in said conduit above said inert fluid, venting said entrapped stored liquid from said conduit and concomitantly therewith introducing more of said inert iiuid to said conduit until the pressure fof the hydrostatic head of said inert liuid in said conduit above the level of said fluid outside said conduit plus atmospheric pressure equals the pressure exerted by the absolute vapor pressure of the stored liquid plus the pressure of the hydrostatic head of said stored liquid within said container on said fiuid outside said conduit, and thereafter withdrawing said pump from and reinserting a pump into said conduit.

4. A method according to claim 3 wherein said stored t i() nigeria wen with wafer, said storage system' thereby v being sealed by said water in said well and liquefied `p5' liquid is liquefied petroleum gas and said inert fluid is water.

5. A method of withdrawing a pump from an underground storage system for liquefied petroleum gas without loss of pressure therein, said liquefied gas exerting a vapor pressure, said system being provided with a closable conduit extending from the surface of the earth to below the bottom of said system, thereby forming` a well at the lower end of said conduit, said conduit com. municating with said system through said well, said pump being suspended within said well by a tubing which extends to the surface of the earth, which comprises, equalizing the pressure between the-upper portions of said conduit and said underground storage system, partially filltroleum" gas being entrapped in said conduit and tubing above said water, venting said entrapped liquefied petrolef um gas and concomitantly therewith introducing more water to said conduit until the pressure of the hydrostatic head4 of the water in said conduit above the water level in said well plus atmospheric pressure equals the pressure exerted by the absoluteV vapor pressure and the hydro-'Qr statlc head of the liquefied petroleum gas within the storv age system on the water in said well, and thereafter with-"' said pump being disposed in the region adjacent the oorf of the cavern, said liquefied gas exerting a vapor pressure, a method for withdrawing said pump from said storage system without the loss of liquefied petroleum gas stored` therein which comprises, introducing water into said cas-f. ing until the water rises in the shaft to cover the lower.A end of said casing, liquefied petroleum gas being entrappedin said casing above the level of the water, venting said entrapped liquefied petroleum gas and concomitantly therewith introducing more water into said casing until` the pressure of thehydrostatic head ofwater in the casing, above the water level in said shaft plus atmospheric pres-l sure equals the pressure exerted by the absolute vapor.y pressure and the hydrostatic head of the liqufied petrole-` um gas within the cavern on said water in said shaft, and thereafter withdrawing said tubing and suspended pump from said casing. t

7. An underground storage system for the storage of liquefied petroleum gas which comprises, in combination, an underground cavern, a shaft extending from the surface of the earth to below the fioor of said cavern to form a well extending below'the oor of said cavern, a casing within the shaft and establishing communication between the surface of the earth and the region of the bottom of said well, a pump suspended by a tubing within the casing, said pump being disposed in the region of said well, a well head sealing said shaft, a casing head sealing the region between the casing and the shaft, a tubing head sealing the region between the tubing and the casing, a first conduit means establishing communication between the interior of said tubing and said space between the tubing and the casing, a valve in said first conduit, a vent in said first conduit and a valve controlling said venta second conduit means establishing communication between said first conduit and said space between the casing and the shaft, a valve controlling said second conduit means,

Va source of Water lunder a pressure greater than the pressure of said liquefied petroleum` gas. in the underground storage system, and a third conduit means establishing communication between said source of water under pressure and said space between the tubing and the casing and a valve controlling said third conduit means.

8. An undergroundestorage system for the storage of liquids under pressure which comprises, in` combination, an underground cavern containing a volatile liquid stored therein under pressure, a shaft extending from the surface of the earth and terminating in a sump at a lower portion of said cavern, a conduit within said shaft extending from a point within said sump to the surface of the earth, means at the surface of the earth sealing the space between said shaft and said conduit, displaceable access means through which a pump can be lowered into or withdrawn from said sump ywithout substantial loss of stored liquid from said cavern comprising a body of inert uid irnmiscible with and having a greater density www 11 than said stored liquid: in said sump covering the lower opening of said conduit and sealing same from communication with said stored liquid, and a column of saidl inert fluid in said conduit, said column being `of just'suicient height that the pressure exerted by the hydrostatic head of said inert uid above the level of said uid in said sump plus atmospheric pressure is about equalvto but not in excess of the pressure exerted on said uid in saidsump by the hydrostatic head plus absolute vapor pressure of said stored liquid, and means forventing stored Vliquid gathered in said conduit above said column of inert fluid.

9. An underground storage system according to claim 8 wherein said volatile liquid is LPG and said inert uid is water.

l0. An underground storage system for the storage of liquid under pressure comprising, `in combination, an underground cavern, a shaft extending fromthe surface of the earth to belowV the Hoor of said cavern to form a well extending below the floor of said cavern, a casing within the shaft and establishing communication between the surface of vthe earth and the region of the bottom of said well, a pump suspended by a tubing Withinl the casing, said pump being disposed in theregion of Said well, means for sealing said shaft, casing and tubing `at the surface of the earth, a source of uid under pressure greater than the pressure in said cavern, said uid being inert, immiscible with and of greater density than said stored liquid, rst conduit means establishing come munication betweenV said source of uid under pressure and the,l space between saidV tubing and said casing, a va'lve controlling said first conduit means', second conduit means venting said space between said tubing and said storage system comprising an underground cavern coil-r taining a liquid exerting a vapor pressure, a shaft extendingY from'the' surface of the earth to the region of the 'oor of said cavern, and a casing within said shaft and establishing communication between the surface of the earth and theregion of the floor of said cavern so that a pump can be inserted into or withdrawn from the lower portion of said casing without loss of pressure from said cavern which comprises partially filling said casing with 4an inert uid which is immiscible with and of greater densityfthan said liquid in said cavern until said uidrises in said shaftto cover the lower end of said casing,` stored liquid therebybeing entrapped in said casing above saidinert uid,`venting said entrapped stored liquid from saidrcasn'g and concomitantly introducing more of .said inert uid into said casing, until the pressure of the hydrostatic head of saidl inert uid in said casing aboveV the level of said luid in said shaft plus atmosphericl pressure equals the pressure' exerted by the absolute vapor pressure of the stored ,liquidl plus the pressure of the hydro-` s 'ta'tic" lieadsof said storedY liquid in said cavern onv said fluid in said shaft.

References enea in theme of this'patent UNITED STATES PATENTS 2,230,830 osberiy s Feb. 4, 1941',- 2',33'/f,4" /2 Kares a r Dec. 2l, 194.34 2,659,209 Phelps -a f Nov. 17, 1953 FOREIGN PATENTS Sweden Apr. 2l, 1942 

1. A METHOD FOR SEALING A CONTAINER WHICH CONTAINS A STORED LIQUID UNDER PRESSURE SO THAT A PUMP CAN BE WITHDRAWN FROM OR INSERTED INTO SAID CONTAINER WITHOUT LOSS OF PRESSURE THEREFROM, SAID LIQUID EXERTING A VAPOR PRESSURE, SAID CONTAINER BEING PROVIDED WITH A CLOSABLE CONDUIT EXTENDING DOWNWARDLY THROUGH A BOUNDARY OF SAID CONTAINER TO A LOWER REGION THEREOF, WHICH COMPRISES, PARTIALLY FILLING SAID CONDUIT WITH AN INERT FLUID WHICH IS IMMISCIBLE WITH AND OF GREATER DENSITY THEN SAID STORED LIQUID, SAID FLUID ATTAINING A LEVEL IN SAID CONTAINER OUTSIDE SAID CONDUIT SO THAT SAID CONTAINER IS THEREBY SEALED BY SAID INERT FLUID, STORED LIQUID THEREBY BEING ENTRAPPED IN SAID CONDUIT ABOVE SAID INERT FLUID, VENTING SAID ENTRAPPED STORED LIQUID FROM SAID CONDUIT AND CONCOMITANTLY THEREWITH INTRODUCING MORE OF SAID INERT FLUID TO SAID CONDUIT UNTIL THE PRESSURE OF THE HYDROSTATIC HEAD OF SAID INERT FLUID IN SAID CONDUIT ABOVE THE UPPER LEVEL OF SAID FLUID OUTSIDE SIDE CONDUIT PLUS ATMOSPHERIC PRESSURE EQUALS THE PRESSURE EXERTED BY THE ABSOLUTE VAPOR PRESSURE OF THE 